Conventionally, mineral-oil-based or wax-based working oil has been used in press-working of aluminum material. However, mineral-oil-based working oil exhibits poor working properties due to lack of ability to form satisfactory oil film, and wax-based working oil exhibits poor degreasing properties due to insolubility of wax in water. Thus, there has been keen demand for development of a metal working lubricant that is excellent in working properties and degreasing properties. Several types of water-soluble metal working lubricants have been disclosed in documents; e.g., a water-soluble metal working lubricant composed of polyoxyalkylene glycol and a dibasic carboxylic acid (Japanese Patent Publication (kokoku) No. 39-14568); a water-soluble metal working lubricant a polybasic carboxylic acid having 14 or more carbon atoms (Japanese Patent Application Laid-Open (kokai) No. 58-160396); a water-soluble metal working lubricant composed of a reaction product of a C12-C42 aliphatic dicarboxylic acid and an alkanolamine (Japanese Patent Application Laid-Open (kokai) No. 61-40400); and a specific phosphate ester (Japanese Patent Application Laid-Open (kokai) No. 2001-214183). However, these water-soluble metal working lubricants are unsatisfactory, and further improvement in properties thereof is demanded.